1. Field of the Invention
The present invention relates to an air-cooled V-type combustion engine having two engine cylinders laid in a V-shape arrangement occupying respective locations that are spaced angularly from each other about an axis of rotation of the combustion engine.
2. Description of the Prior Art
It is well known that an air-cooled vertical V-twin combustion engine has long been used as a drive source for a work machine such as, for example, a brush cutting machine. This known air-cooled V-twin combustion engine has a cooling air passage defined in a fan casing, through which a cooling air induced by a cooling fan assembly flows to cool the two engine cylinders.
It has, however, been found that since the cooling air, before it is used to cool the engine cylinders, flows radially outwardly and slantwise from a trailing side towards a leading side, or forwardly, with respect to the direction of rotation of the cooling fan assembly, one of the two engine cylinders, which is positioned on the leading side with respect to the direction of rotation, tends to be cooled with an insufficient amount of cooling air although the other of the two engine cylinders, which is positioned on the trailing side with respect to the direction of rotation of the cooling fan assembly is cooled sufficiently. This leads to a difference in temperature between the two engine cylinders, which in turn results in a difference in combustion condition occurring in those two engine cylinders, and, therefore, disadvantages and inconveniences tend to occur in connection with thermal efficiency and removal of obnoxious components of the exhaust gases.
In view of the above, the Japanese Laid-open Patent Publication No. 61-106968, first published May 24, 1986, has suggested an air-cooled V-twin combustion engine system, in which two spiral guide walls for separating and guiding the cooling air, induced by the cooling fan assembly, towards the two engine cylinders, respectively, are formed in an inner surface of the fan casing so as to protrude in a direction parallel to the axis of rotation of the cooling fan assembly.
It has, however, been found that in the prior art combustion engine system discussed above, the cooling air tends to leak in a direction radially of the cooling fan assembly from a free end of the guide walls protruding in a direction parallel to the axis of rotation of the cooling fan assembly, it is not easy to enable the cooling air to be supplied towards the two engine cylinders in a desired proportion.